Introduction
Overpopulation is an issue that bothers economists and people around the world for a long time. It was popularised in 1968 by Pail Ehrlich with the release of the book “Population Bomb”, which predicted worldwide famines due to overpopulation [1].
Figure 1 shows an extremely rapid growth in the world population since the eighteenth century. In the last 20 years, the global population size increased by around 1.6 billion people. [2] Even though Ehrlich's beliefs were disproved and the world economy did not collapse, the conversations about optimal population and whether our current population is the optimal one did not cease.
Optimal is the state of being most favourable or satisfactory. Additionally, optimal in the case of the population is that the population should be sustainable and not volatile, which means that the population will remain stable and won’t change rapidly. The sustainability can be further defined in many ways: economic sustainability, environmental sustainability, demographic stability and stable provision of services. In this essay, I will look at different factors that should be considered when determining an optimal population.
Malthusian Theory of Population
Firstly I want to talk about the Malthusian theory of population. Thomas Robert Malthus was an English economist and demographer. He was one of the first to share his concerns about population growth. In 1798 Malthus published anonymously the first edition of An Essay on the Principle of Population as It Affects the Future Improvement of Society (1798). He stated that an increase in population, if left unchecked, will increase in geometric progression, however, subsistence (food and other supplies needed for survival) increases only in an arithmetic progression. This means that the population would always tend to outrun the production growth [4]. societies that ignored the imperative for moral restraint (preventive checks) - delayed marriage and celibacy for adults until they were economically able to support their children - would suffer the deplorable positive checks of war, famine or epidemic, that would bring the population down to the point of crisis, as seen on Figure 2 [5]. This is called the Malthusian trap.
Thomas Malthus was a pessimistic economist and due to this, he failed to acknowledge the agricultural revolution, which caused food production to meet and exceed the population growth, which allowed many countries to escape the Malthusian trap [6].
Optimum Theory of Population
Malthusian theory was rejected and replaced by the Optimum Theory of Population. The optimum theory of population was propounded by Edwin Cannan, an English Economist of the London School of Economics in his book ‘Wealth’ published in 1924 and popularised by Robbins, Dalton and Carr-Saunders [7]. While Malthusian theory looks at the relationship between population growth and food supply, the Optimum Theory of Population looks at the relationship between population size and the production of wealth [8]. Cannan defined the optimum population as the ideal population which combined with other available resources for means of production of the country that yield the maximum returns or income per head [9].
This can be demonstrated on a diagram (Figure 3).
When the population is ON, it uses the resources available to maximise income per capita, which means that is the optimal population. When the population is lower than the optimum, for example, OB, the population size is insufficient to exploit the resources to its maximum efficiency, there is some spare capacity and productive efficiency is not reached. Therefore income per capita is lower. Alternatively, when there is overpopulation (OD), the economy’s efficiency falls to give only a subsistence income to the labour force [10]. The optimal population point is not static and changes over time. There can be an increase in the productive potential, for example, improvements in technology. This will cause the level of income per head related to the size of the population to shift from AP to AP1, which causes the optimal population size to increase from ON to ON1 (Figure 4).
However, the model has some drawbacks. First of all, it is challenging to find out the optimal population as there are many variables to consider, for example, capital stock, technical knowledge and natural resources. Secondly, the model is not realistic as it assumes that as a country's population increases, the natural resources, the capital stock and the state of technology remain unchanged, which won’t happen in a real-life scenario. Finally, the model only looks at the economic factors and does not consider factors like environmental sustainability, political considerations and others [13].
Environmental Sustainability
As I stated previously, environmental factors also can be considered when determining the optimal population. As the global population rises, the demand for food rises, which puts pressure on land, water, and energy. In addition, it leads to more chemical fertilisers and pesticides being used which ultimately leads to soil deterioration.
In regions where people depend on subsistence farming (when farmers cultivate crops for their own consumption and that of their families), more land must be cleared for crops due to the lack or absence of irrigation, seed, and soil improvement. This leads to deforestation and soil health and affects the balance of carbon on the planet. Furthermore, deforestation leads to habitat loss and can have a negative effect on biodiversity. As consumption patterns change, so do people’s diets. With a rise in average incomes, the change in the food that people eat has been shifting towards the consumption of more calories and a wider variety of resource-intensive foods (beef, dairy, poultry, pork, eggs). Such changes have a detrimental effect on the environment causing a rising level of greenhouse gas emissions and contamination of the water and soil due to poor environmental mitigation. [14]
Population growth is one of the drivers of increasing emissions. The burning of fossil fuels, which have provided most of the energy needed for economic development, releases GHGs, mainly in the form of carbon dioxide (CO₂). This leads to global warming, which increases the amount of natural disasters, like droughts, hurricanes and floods due to ice sheets shrinking and loss of habitats. [15]
However even though the population increase has an impact of increasing emissions, it might not be the main factor. As was stated by the UN, as of 2021, high-income and upper-middle-income countries, which together comprise 48 per cent of the world’s population, were responsible for about 82 per cent of the CO₂ added to the atmosphere each year, as can be seen in Figure 5.
Low-income and lower-middle-income countries, where most future population growth is projected to take place, have so far contributed significantly less to these emissions.[16] This means that income is a more important factor, as the higher the income, the more people consume, leading to more Greenhouse gasses emitted.
Provision of Services
Quality of life also can be considered when deciding the optimal population. Even though there are a lot of ways to describe quality of life, I would like to focus on the provision of services, like healthcare and education.
Communicable diseases, conditions arising during pregnancy and childbirth, and nutritional deficiencies are among the leading causes of death and illness in many of the low-income and lower-middle-income countries where the population is growing rapidly [18].
Achieving universal health coverage is critical for reducing inequalities in health both between and within countries and for promoting higher quality of life globally. Countries experiencing rapid population growth tend to have low coverage of essential healthcare services (can be seen in Figure 6).
As a result, individuals in those countries are less likely to have financial risk protection and access to quality healthcare services, including for essential medicines and vaccines, which reduces their quality of life [19]. Most of the countries with the lowest coverage of essential healthcare services are in sub-Saharan Africa. For many low-income and lower-middle-income countries where essential services are lacking, rapid population growth may pose a significant challenge to achieving the target of universal access to health care. Because of their rapid population growth, these countries will need to invest substantially in their healthcare systems. If countries are successful in this regard, in addition to a healthier population, there would be the added benefit of generating millions of jobs in the healthcare sector, which would lead to a fall in unemployment [20]. From Figure 6, the higher the population growth rate in the country, the lower the coverage of healthcare services. This means if the population rate is lower, the government can manage the increases in the provision of health care required, leading to higher standards of living.
Education is not only essential for improving standards of living, it is an important investment to promote sustainable development. Education boosts human capital accumulation, promotes faster economic growth and greater productivity, advances gender equality and improves health outcomes.[21]. Yet, despite of the well-established social and economic returns to education, a quarter of a billion children, adolescents and youth in 2018 did not have access to education [22].
For low-income and lower-middle-income countries with growing cohorts of children and youth, ensuring access to a quality education presents a significant challenge [23]. In sub-Saharan Africa, for instance, despite robust gains in school enrolment percentages in recent decades, the number of children who are not in school has remained largely unchanged owing to continued population growth [24]. As can be seen in Figure 7, The higher the population growth rate, the less government expenditure per student in primary and secondary education in that particular country.
This means that due to higher population sizes in lower-income countries, more funding is required for the education sector. However, due to insufficient government spending, the quality of education falls, which might lead to a decrease in economic growth and development and lower living standards of individuals.
Demographic stability
Demographic stability is also a factor that should be looked at when searching for an optimal population.
As I said earlier, for a population to be optimal it should be sustainable over a long period of time. For that to happen it’s important to have a stationary population structure, with an equal population in each age group. This means the birth and death rates are equal and the population is neither increasing nor decreasing. There are usually not many major changes in the mortality rate and fertility rates [25]. This can be demonstrated in a population pyramid.
An example of a country with a stationary population pyramid is the USA. Looking at Figure 8, the population is evenly distributed between the age groups, understandably decreasing as the people get to 70 years.
What should be avoided are expansive and constrictive pyramids. An example of a country with a constrictive population pyramid is China. This is due to the implementation of the one-child policy, The one-child policy was designed in 1980 as a temporary measure to put a brake on China’s population growth and to facilitate economic growth under a planned economy that faced severe shortages of capital, natural resources, and consumer goods [28].
Because of the policy, as can be seen in Figure 9, the median age moved from 29 in 2000 to around 37 years in 2020 [29]. Therefore, China faces the challenge of supporting its outsized ageing population with a diminishing working-age population [30].
Conclusion
An optimal population combines and finds a balance between different factors. It can be demonstrated in the diagram. The optimal population should be maintained over a long period of time using a stationary population structure. The quality of life is maximised through sufficient provision of services by governments having enough funding and sufficient income per capita, but with minimal impact on the environment such that sustainability and biodiversity also are maximized.
This point is represented in Figure 10 by the letter A. The letter B represents our current condition, where population pressure is already reducing the quality of life and biodiversity in most of the world [32]. This means the optimal population is lower than our current one.
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